Description of problem:
When a VM's disks are on more than 1 storage domain, it is nearly impossible to import the disks from the second domain.

Version-Release number of selected component (if applicable):
ovirt-engine-4.3.10.4-1

How reproducible:
Always

Steps to Reproduce:
1. Migrate OS & databased disks on one storage domain 
2. Migrate another disk from the same vm to another storage domain 
3. Detach the second (data ) domain
4. Try to import the VM from the second (data ) domain -> fails due to same VM ID
5. Delete the VM's snapshots on the non-data disks (first storage domain)
6. Detach the disks
7. Delete the VM
8. Import the VM from the second (data) storage domain
9. Delete the VM's snapshots in order to equalize the data disks to the level of the non-data disks
10. Attach the non-data disks to the VM


Actual results:
The end user has to delete the VM's snapshots in order to be able to delete the VM without deleting the original non-data disks. Once the VM is also deleted , the user can import the data disks via the 'Import VM' (from the second storage domain). Still, the user has again to delete the snapshot for the data disks and only then can merge the non-data and the data disks.

Expected results:
There should be a way to import the data disks from the second data storage without having to delete the VM's snapshots.
When the VM has to be migrated to another oVirt Engine (via export domain) , the user has to 'Import VM' with the option partial for the first storage domain and then he/she has to wipe the snapshots + VM (non-data disks detached) just to be able to import the VM's data disks from the second storage domain.

It will be way better if one of the following is implemented:
- merge/squash to identical partial VMs
- Override an existing VM
- Force import the VM with a different ID

For details , please check: 
https://lists.ovirt.org/archives/list/users@ovirt.org/message/WTJXOIVDWU6DGVZQQ243VKGWJLPKHR4L/